The present invention relates to an improved magnetoresistive effect element for reading out of informations magnetically stored in a magnetic recording medium, and an improved magnetoresistive effect sensor using the magnetoresistive effect element.
The magnetoresistive effect element is capable of sensing variations of resistance, which may be regarded to be a function of intensity of magnetic flax. The magnetoresistive effect sensor is capable of detecting magnetic signals through the magnetoresistive effect element for reading out of data magnetically stored in a magnetic recording medium at a large linear density. The conventional magnetoresistive effect element utilizes the anisotropic magnetoresistive effect element which is defined to be a phenomenon of variation in resistance of the element proportionally to a square of cosine of an angle defined between a magnetization direction and a sensing current flowing through the element. The anisotropic magnetoresistive effect is described in detail by D. A. Thomson et al. "Memory Storage and Related Applications", IEEE Transaction on Mag. MAG-11, p. 1039 (1975). The magnetoresistive effect sensor using the magnetoresistive effect element is often applied with vertical bias in order to suppress Barkhausen noises. This vertical bias may be applied to anti-ferromagnetics such as FeMn, NiMn, and nickel oxide.
In recent years, a magnetoresistive effect element having a spin valve film has been developed. Such magnetoresistive effect element having a spin valve film utilizes a giant magnetoresistive effect. This giant magnetoresistive effect is a phenomenon of variation in resistance of the element both due to a spin-dependent transmission of conduction electrons between ferromagnetic layers which sandwich a non-magnetic layer and due to a spin-dependent scattering of the conduction electrons on interfaces between the ferromagnetic and non-magnetic layers. This magnetoresistive effect element shows variation in plane resistance between the ferromagnetic layers isolated by the non-magnetic layer in proportional to cosine of an angle defined between the magnetization directions of the two ferromagnetic layers. As compared to the anisotropic magnetoresistive effect element, the giant magnetoresistive effect element is improved in the sensitivity and shows a larger variation in resistance.
In Japanese laid-open patent publication No. 2-61572, it is disclosed that a laminated magnetic structure shows a large magnetoresistance variation due to anti-parallel order of magnetization in the magnetic layers. Ferromagnetic transition metals and alloys thereof are available for the laminated structure. It is further disclosed that an anti-ferromagnetic layer is added to one of the paired ferromagnetic layers isolated by the intermediate layer. FeMn is suitable for the anti-ferromagnetic layer.
In Japanese laid-open patent publication No. 4-358310, it is disclosed that the magnetoresistive effect element has two thin ferromagnetic layers isolated by a thin non-magnetic metal layer, where if an applied magnetic field is zero, then the magnetization directions of the two ferromagnetic thin layers are different by the right angle. The two ferromagnetic layers isolated from each other by the intermediate layer vary in resistance in proportional to cosine of an angle defined between the magnetization directions of those two layers but independently from a direction of current flowing through the sensor.
In Japanese laid-open patent publication No. 6-203340, it is disclosed that the magnetoresistive effect sensor has two ferromagnetic thin layers isolated by a non-magnetic metal thin layer, where if an externally applied magnetic field is zero, then anti-ferromagnetic layers adjacent to each other are kept to differ in magnetization direction by the right angle.
Either if the anti-ferromagnetic layer is used as a vertical bias layer for obtaining a magnetic stability or if the anti-ferromagnetic layer is used for the magnetoresistive effect element having the spin valve film, then FeMn is mainly used as being likely to be oxidized in atmosphere. For this reason, in order to practice the element, it is essential to add an additive or use a protection film. Notwithstanding, deterioraten in characteristic or properties of the element is caused in fabrication processes. The reliance of the conventional magnetoresistive effect element would be insufficient.
On the other hand, if NiO film or CoPt superior in corrosion resistance film is used reliance is used, then other problem is raised that hysteresis is likely to appear on the R-H loop.
If the nickel oxide based film such as FeMn, NiMn, IrMn, PdPtMn, or ReMn is used for the anti-ferromagnetic layer and if Ni-based, Fe-based, Co-based alloys are used for a pinned magnetic layer, then the following problems are raised. If the magnetic field is applied in a direction different from such a direction as to allow a uni-directional anisotropy at 100-200.degree. C., then the magnetization of nickel oxide is inverted to the direction of the magnetic field. This means that the magnetic recording device is not useable at a high temperature of not less than 70.degree. C., for which reason the reliance of the magnetic recording device would be insufficient.
In the above circumstances, it had been required to develop an improved magnetoresistive effect element free from the above problems and disadvantages, and a novel magnetoresistive effect sensor using the improved magnetoresistive effect element.